Definitions

A statistic is a numerical measure (or a function) that describes a characteristic of the sample.

A parameter is a numerical measure that describes a characteristic of the population.

We use statistics to estimate parameters.

We use sample-statistics to estimate/understand population parameters or characteristics!

Example

Suppose we are interested in the meancalory or mean sodium content of hot dogs. It would be difficult to obtain measures of calory and salt content for ALL hot-dogs. However, we can use the Hot dogs datafile that we discussed uearlier. This data contains a sample of 54 major hot dog brands. Some of the interesting population papameters are the mean-calory, mean-sodium, variance-of-calory between hot-dogs and variance-of-sodium between hot-dogs. These measures may be estimated from the sample using the corresponding sample-statistics (sample-averages and sample-variances).